An electronic timer or time-programming apparatus can comprise an electronic clock with pulse generator and several divider stages, a central unit with read/write or read-only working memories, a calculating--i.e. arithmetic logic--unit for data processing, as well as a program memory with associated program-counting and decoding devices; further, a luminous-digit arrangement, an input unit with operating elements such as keys and switches, an output unit for the activation or deactivation of switching devices for load circuits; and, finally, control and current-supply assemblies as well as a housing in whose front wall operating and setting fields and at least one luminous-digit device are disposed.
In recent times the demands made on a timing or time-programming apparatus, especially switching clocks with electromechanical drive and mechanical switching devices such as radially displaceable switching segments, plug-in connecting pins or the like, have become ever more exacting. Thus, at present and increasingly so, one expects at least several time-switching programs, i.e. with differences for each day of the week and also for different switching channels with partly different time-switching programs, to be easily and correctly settable.
To be sure, electronic timers have lately been introduced into the market with sophisticated multiply interdigitated time and channel programs; it has been shown, however, that these programs are susceptible in various ways to the input of erroneous instructions and that their correction entails problems since, for example, whole sections of the switching program must be erased and the corresponding switching data must be fed in again from the beginning. Thus, e.g. with the known electronic time switch "GRAESSLIN digi 127", it is possible to load it with impermissible time data, such as a response at 26.84 hours for weekday "9", because of the use of a decimal keyboard for the infeed of the switching-time data; while such error is indicated by flashing, it still requires an erasure of the entire time input and its repetition in a prescribed and fixed sequence, i.e. from the beginning.
Furthermore, with the known time switch it is not possible to feed in and indicate a complete set of switching data, but only a partial section thereof, e.g. for a single weekday and with either an ON or an OFF switching time; combinations such as several weekdays with the same ON and OFF switching times can be neither displayed nor simultaneously checked. The instructions for use are accordingly conveyed in a specimen programming sheet.